Optically active carbonyl compounds are important intermediates for synthesizing medicine, essences & flavors and pesticides. Whereas to conduct selective asymmetric hydrogenation reaction to the carbon-carbon double bond of α, β-unsaturated carbonyl compounds is an important approach for obtaining optically active carbonyl compounds. Chemists have developed various methods to conduct selective asymmetric hydrogenation reaction to the carbon-carbon double bond of α, β-unsaturated carbonyl compounds, such methods and their existing technical shortcomings are as follows:
(1) Homogeneous catalytic reactions adopting hydrogen as hydrogen source, since such methods hydrogenate carbon-carbon double bond with hydrogen using catalytic amount of homogeneous catalysts without adding reaction promoters, the catalysts can be recycled without producing a large amount of by-products. CN101675020 introduces a method for synthesizing optically active carbonyl compounds and the application of such method in preparing optically active (R)-citronellal. Such method uses the air-sensitive phosphine ligand chiraphos, and the reaction gas needs to use a certain proportion of CO and hydrogen, meanwhile, in order for the catalyst to be recycled, the catalysts need to be regenerated under certain conditions (Asymmetric Catalysis on Industrial Scale, ed. Blaser, H.-U., H.-J. Federsel. Wiley-VCH, Weinheim, Germany, 2010, pp. 187-205).
(2) CN103249484 describes a method that prepares optically active carbonyl compounds through heterogeneous metal catalytic reactions using hydrogen as hydrogen source, such method adopts catalysts such as metal catalyst, chiral cyclocompound and acid, and its reaction mechanism may involve double catalytic cycles (Chem. Commun., 2012, 48, 1772-1774). Although heterogeneous metal catalysts can be easily recycled from the reaction solution, non-ideal phenomena such as loss or inactivation may occur in the reaction solution.
(3) Asymmetric hydrogenation reaction that uses dihydropyridine compound as a negative hydrogen source to transfer hydrogen from α, β-unsaturated carbonyl compounds is another important method for preparing optically active carbonyl compounds. In 2005, MacMillan adopted this method and used stoichiometric dihydropyridine compounds to selectively transfer the negative hydrogen into the double bond of the unsaturated aldehyde, obtaining optically active β-substituted aldehyde (J. Am. Chem. Soc., 2005, 127, 32-33). In 2006, Benjamin List reported a method that prepares optically active carbonyl compound using chiral organic salt as catalyst and dihydropyridine compound as negative hydrogen source, which is primarily characterized in that: the chiral organic salt catalyst consists of chiral phosphate negative ion and achiral ammonium ion, and the dihydropyridine compound dosage is stoichiometric amount (Angew. Chem. Int. Ed. 2006, 45, 4193-4195). CN103724170 describes a method that asymmetrically synthesizes dextro-citronellal using citral as an initial material, such method also adopts stoichiometric dihydropyridine compound as a negative hydrogen source. The reason why stoichiometric dihydropyridine compound is required is that dihydropyridine compound will eventually become pyridine compound in the reaction system, therefore, dihydropyridine compound is non-recyclable hydrogen source in the reaction system, meanwhile, a large amount of dihydropyridine compound residues are left in the reaction system and are difficult to be separated from the target product, this is obviously against the economical rule.
Therefore, in order to overcome the technical problems existing in the above mentioned prior arts, a new method that is easier to operate, has moderate reaction condition and is more economical for preparing optically active carbonyl compound needs to be developed. Such a new method needs to satisfy the following characteristics: the catalysts can be easily recycled, and the original reaction activation level can be maintained; if a dihydropyridine compound is used as a negative hydrogen source, it shall be used as less as possible. Yonggui Zhou's research group (CN104710377) adopts biomimetic asymmetric catalysis technology to use the combination of hydrogen-metal Ru catalyst-catalytic amount of pyrroline[1,2-a]quinoxaline to asymmetrically hydrogenate the carbon-nitrogen double bond of unsaturated imine. Currently, this biomimetic asymmetric catalyst technology is primarily used for the asymmetric hydrogenation reaction of the carbon-nitrogen double bond of unsaturated imine, and no literature report on its application in asymmetric hydrogenation reaction of carbon-carbon double bond of unsaturated carbonyl compound yet.